It has been known an organic electroluminescence element having a configuration shown in FIG. 7 (see e.g. JP2006-331694A; Patent Document 1). This organic electroluminescence element includes: one electrode (cathode) 101 disposed on a top surface of a substrate 104; a light emission layer 103 disposed on a top surface of the electrode 101 with interleaving an electron injection/transport layer 105 therebetween; and the other electrode (anode) 102 disposed on the light emission layer 103 with interleaving a hole injection/transport layer 106 therebetween. This organic electroluminescence element includes a sealing member 107 on the top surface side of the substrate 104. With this organic electroluminescence element, the light that is emitted from the light emission layer 103 passes through the electrode 102 that is designed as an optically transparent electrode and through the sealing member 107 formed of a transparent body, and then is radiated outward.
The electrode 101 is designed as a light reflective electrode, and is made of e.g. Al, Zr, Ti, Y, Sc, Ag, or In. The electrode 102 of the optically transparent electrode is made of e.g. indium tin oxide (ITO) or indium zinc oxide (IZO).
In an organic electroluminescence element, it needs a large electric current in order to obtain a high-brightness light. However, in a general organic electroluminescence element, the anode formed of an ITO film has a larger sheet resistance than that of the cathode formed of a metal film, an alloy film, a metal compound film or the like. Therefore, the anode has a larger potential gradient. Thus, the prior (general) organic electroluminescence element has a large unevenness of brightness in the in-plane direction.
In order to overcome the problem of the electroluminescence lamp including the electrode of an ITO film that is formed by sputtering, it has been proposed an electroluminescence lamp including an electrode that is formed of a material other than ITO (see JP2002-502540A; hereinafter referred to as Patent Document 2). Patent Document 2 discloses an electroluminescence lamp 210 that includes a first conductive layer 220, an electroluminescent material 230, a second conductive layer 240, and a substrate 245. The first conductive layer 220 is formed in a shape of a rectangular grid electrode provided with rectangular-shaped openings 250, as shown in FIG. 8.
Patent Document 2 describes that the first conductive layer 220 and the second conductive layer 240 are preferably made of conductive ink such as silver ink, copper ink or the like. Patent Document 2 describes that the first conductive layer 220, the electroluminescent material 230, and the second conductive layer 240 are formed by screen printing, offset printing or the like.
Patent Document 2 describes that if a uniform brightness lamp 210 is required the density of openings 250 should be approximately constant over the lamp's surface.
In the electroluminescence lamp 210 shown in FIG. 8, the first conductive layer 220 has the openings 250. Therefore, “carrier” is injected from the first conductive layer 220 into the electroluminescent material 230 only through a region which overlaps with the first conductive layer 220. Therefore, in this electroluminescence lamp 210, the electroluminescent material 230 has an inferior luminous efficiency at regions corresponding to the openings 250. As a result, this electroluminescence lamp 210 has a concern that the external quantum efficiency becomes low.